1. Technical Field
The present invention relates to an image display device such as a projector and a method of controlling the image display device.
2. Related Art
The image display device such as a projector is provided with a light modulator such as a liquid crystal light valve or a mirror device for each of the color components of R (red), G (green), and B (blue) of a display target image. Further, image signals of sub-pixels of the respective color components of R, G, and B constituting a plurality of pixels in the display target image are provided to the light modulators corresponding respectively to the color components, and output light beams of the respective light modulators are combined with each other via an optical system to irradiate a display surface. In such a manner, the images of the respective sub-pixels different in color component are displayed on the display surface in an overlapping manner.
Here, if the number of pixels of a display image by the projector is increased, positioning of each of the sub-pixels by the optical system tends to become difficult. For example, a projection lens provided to the projector has chromatic aberration, and the refractive index thereof varies with the wavelength. Therefore, high aberration accuracy is required with respect to the optical system provided to the projector. However, it is difficult to accurately adjust all of the display positions of the sub-pixels constituting one pixel. Therefore, there occurs position shift in which the display positions of the sub-pixels corresponding to the respective color components are shifted from the reference positions.
The direction and the distance of such a position shift of the sub-pixel are generally different between the sub-pixels of the respective color components corresponding to the same pixel. Therefore, there occurs a problem that the original color represented by the image signal is not displayed.
Therefore, in the technology described in JP-A-2009-122156 (Document 1), it is arranged that the position shifts of the display positions from the reference positions are obtained with respect to the sub-pixels of the display target image, and a pixel displacing correction based on the position shifts is performed on the image signal to be supplied to the respective light modulators to thereby perform compensation of the position shifts of the display positions of the sub-pixels. Here, in the pixel displacing correction, by performing an interpolation operation using the image signals of the respective sub-pixels of the display target image, there are generated image signals obtained by moving the images of the respective sub-pixels in opposite directions to the directions of the position shifts and as much as the same distances as the distances of the position shifts, respectively.
Incidentally, when performing the pixel displacing correction described above, a part or the whole of the sub-pixels located in the vicinity of the boundary of the effective display range in the display target image is located outside the effective display range, and is therefore not displayed, and the display luminance of the sub-pixels decreases in some cases. In this case, in the case in which sub-pixels of other color components belonging to the same pixel as the sub-pixel are located within the effective display range, and there is no decrease in display luminance, there is a problem that coloring occurs in the pixel.
In order to solve this problem, there is adopted, in some cases, a measure of disposing superfluous pixels (hereinafter referred to as parting pixels) outside the effective display range in addition to the pixels in the effective display range. In the example shown in FIG. 14, there are disposed two parting pixels Mi outside the effective display range with respect to each of the color components of R, G, and B. In this case, since it is possible to display the image of the sub-pixels having been located outside the effective display range using the parting pixels Mi due to a pixel displacing correction, it is possible to prevent coloring of the pixels in the vicinity of the boundary of the effective display range from occurring. In the example shown in FIG. 15, the pixel displacing correction is not performed with respect to the G component, and the pixel displacing correction for matching the display positions of the sub-pixels with the display positions of the sub-pixels of the G component is performed with respect to each of the R component and the B component. In this example, since in FIG. 14, the sub-pixels of the R component are shifted as much as 1 pixel to the left with respect to the sub-pixels of the G component, there is performed the pixel displacing correction for moving the image signal of the R component as much as 1 pixel to the right as shown in FIG. 15 using the parting pixels Mi located on the right side of the sub-pixels (the N-th sub-pixels) located on the right end of the effective display range. Further, in this example, since in FIG. 14, the sub-pixels of the B component are shifted as much as 2 pixels to the right with respect to the sub-pixels of the G component, there is performed the pixel displacing correction for moving the image signal of the B component as much as 2 pixels to the left as shown in FIG. 15 using the two parting pixels Mi located on the left side of the sub-pixels (the first sub-pixels) located on the left end of the effective display range.
However, in order to adopt this measure, it is necessary to provide elements corresponding to the parting pixels outside the effective display range to the light modulator such as a liquid crystal light valve or a mirror device in addition to the elements corresponding to the pixels in the effective display range.
For example, in the case of the liquid crystal light valve compatible with 1080 p, there are 1920×1080 pixels in the effective display range. If it is attempted to add two parting pixels in each of upper, lower, right, and left directions outside the effective display range, the total number of pixels increases to 1924×1084. As described above, in the case of providing the parting pixels in order to prevent the coloring, it is necessary to provide the light modulators with the element corresponding to the parting pixels, and there arises a problem that the light modulators grow in size accordingly. Further, in the case of not using the parting pixels for the image display, the light irradiation on the elements corresponding to the parting pixels in the light modulator is not blocked, but the image signal to be supplied to the elements corresponding to the parting pixels is only changed to an image signal corresponding to black display. Therefore, there arises a problem that a black frame corresponding to the parting pixels performing the black display is visually recognized depending on the contrast of the display target image. Due to such circumstances, there also exist a lot of projectors not provided with the parting pixels.
However, when performing the pixel displacing correction in the projector not provided with the parting pixels, there arises a problem of coloring in the vicinity of the boundary of the effective display range described above. FIG. 16 shows a problem, which arises in the case of not providing the parting pixels Mi in the situation shown in FIG. 14 and FIG. 15. In this example, since the parting pixels Mi do not exist, the sub-pixel (the N-th pixel) on the right end of the R component is placed outside the effective display range due to the pixel displacing correction, and is therefore not displayed. Further, the two sub-pixels (the first and second sub-pixels) on the left end of the B component are placed outside the effective display range due to the pixel displacing correction, and are therefore not displayed. Therefore, in the case of, for example, displaying the effective display range with solid white, the central part thereof becomes a white display area 200W, but a yellow display area 200Y having a stripe shape with a width of two pixels occurs at the left end, and a blue display area 200B having a stripe shape with a width of one pixel occurs at the right end.
Therefore, in the past, there has been required a measure of using the projector without providing the parting pixels to the projector, and while allowing the occurrence of the coloring in the vicinity of the boundary of the effective display range, or a measure of providing a small number of parting pixels to the projector to limit the pixel displacing correction within the range determined in accordance with the number of parting pixels.